Hint at buffer list on left when no buffer chosen

Steps

1. Disconnect QuasselDroid, clear from Recents (remove any saved activity state)
2. Connect to core
3. Hide buffer list without choosing a buffer

Expected

The area where chat history would normally show contains a graphic and brief text hinting at the buffer list.

For example...

Let's get talking

Pick a conversation on the left

...below an icon of an arrow above a list pointing to the left, perhaps a cross between the list icon and the arrow_left icon.

But with more suitable phrasing and icon.

Actual

The area where chat history shows is blank, no clues given for the next step.

Additional

Even if the buffer list always opened, it may be more friendly to nudge towards the left sidebar.

Example screenshot of the Transistor radio app with no stations added